There exist many gain stages that will provide a constant gain of the input signal over a wide range of input voltages. These are commonly known as gain amplifiers. Moreover, there are many circuits that provide a constant output voltage level over a wide range of input voltages. These circuits are commonly called automatic level control circuits.
However, few, if any, of these circuits provide a constant gain for a first range of input voltage signals, and a constant, undistorted and unclipped output voltage level for a second range of input voltage signals.
At least one attempt that prior art has made in providing a gain stage circuit having both a fixed gain function and an automatic level control function is to monitor the output voltage of the gain stage circuit via external components such as resistors, capacitors and operational amplifiers. However, the disadvantage of this method is that by monitoring the output voltage, the output voltage level during the automatic level control mode is not stable because it is being monitored only after a change occurs. Thus, the automatic level control function does not provide a substantially constant output voltage.
Hence, there exists a need to provide a gain stage circuit for alternately providing a fixed gain for a first range of input voltage signals, and for providing a constant output voltage for a second range of input voltage signals.